Instructions
Equip your Stinger missiles and aim for the heads of the Metal Gear RAYs. You can also hit their legs too. This will not cause damage, but will prevent them from attacking you if you do not have enough time to aim for the head.
Toss a Chaff Grenade at the Metal Gear RAYs to stun them and get ready to dodge when they shoot their missiles at you. As long as you keep moving, you should avoid damage.
Fire more Stinger missiles at the RAYs when you have time, after dodging their attacks. Eventually, one will jump on the platform near you.
Move as far away as possible from the RAY on the platform because it will try to shoot you with missiles from its legs.
Fire Stinger missiles at it to prevent the attack, while also continuing to fire at the RAYs on the other platform.
Destroy five RAYs to end the boss battle and level if you play the game on the "Normal" difficulty. You will have to kill 20 of them on "Hard" and 25 on "Extreme" to finish the fight.